iOS NFC: Always ensure timeout after session invalidation

iOS needs some time after invalidating a session before a new session
can be started. Otherwise the NFC dialog of iOS will not show up.

For restarting a session inside the iOS NearfieldManager, this was
already solved with a timeout of 2 seconds.

This commit fixes the case, that a user of the Nearfieldmanager
restarts a session manually too fast.

Change-Id: Ic91ad225a9cab13ba92523f33a19f44af68575a0
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
(cherry picked from commit 849ba86ba9a073a266219b6a39786e20f4f3ed7b)

2 files changed, 34 insertions, 15 deletions

diff --git a/src/nfc/qnearfieldmanager_ios.mm b/src/nfc/qnearfieldmanager_ios.mm
index 6fd71451..a0651626 100644
--- a/src/nfc/qnearfieldmanager_ios.mm
+++ b/src/nfc/qnearfieldmanager_ios.mm
@@ -25,6 +25,10 @@ QNearFieldManagerPrivateImpl::QNearFieldManagerPrivateImpl()
     connect(this, &QNearFieldManagerPrivateImpl::didInvalidateWithError,
             this, &QNearFieldManagerPrivateImpl::onDidInvalidateWithError,
             Qt::QueuedConnection);
+
+    sessionTimer.setInterval(2000);
+    sessionTimer.setSingleShot(true);
+    connect(&sessionTimer, &QTimer::timeout, this, &QNearFieldManagerPrivateImpl::onSessionTimer);
 }
 
 QNearFieldManagerPrivateImpl::~QNearFieldManagerPrivateImpl()
@@ -62,7 +66,7 @@ bool QNearFieldManagerPrivateImpl::startTargetDetection(QNearFieldTarget::Access
         if (@available(iOS 13, *))
             if (NFCTagReaderSession.readingAvailable) {
                 detectionRunning = true;
-                startSession();
+                scheduleSession();
                 return true;
             }
         return false;
@@ -71,16 +75,28 @@ bool QNearFieldManagerPrivateImpl::startTargetDetection(QNearFieldTarget::Access
 
 void QNearFieldManagerPrivateImpl::stopTargetDetection(const QString &errorMessage)
 {
-    if (detectionRunning) {
-       stopSession(errorMessage);
-       detectionRunning = false;
-       Q_EMIT targetDetectionStopped();
-    }
+    if (!detectionRunning)
+        return;
+
+    isSessionScheduled = false;
+    stopSession(errorMessage);
+    detectionRunning = false;
+    Q_EMIT targetDetectionStopped();
 }
 
+void QNearFieldManagerPrivateImpl::scheduleSession()
+{
+    if (sessionTimer.isActive()) {
+        isSessionScheduled = true;
+        return;
+    }
+
+    startSession();
+}
 
 void QNearFieldManagerPrivateImpl::startSession()
 {
+    isSessionScheduled = false;
     if (detectionRunning)
         if (@available(iOS 13, *))
             [delegate startSession];
@@ -132,17 +148,11 @@ void QNearFieldManagerPrivateImpl::onTargetLost(QNearFieldTargetPrivateImpl *tar
 void QNearFieldManagerPrivateImpl::onDidInvalidateWithError(bool doRestart)
 {
     clearTargets();
+    sessionTimer.start();
 
     if (detectionRunning && doRestart)
     {
-        if (!isRestarting) {
-            isRestarting = true;
-            using namespace std::chrono_literals;
-            QTimer::singleShot(2s, this, [this](){
-                        isRestarting = false;
-                        startSession();
-                    });
-        }
+        scheduleSession();
         return;
     }
 
@@ -150,4 +160,10 @@ void QNearFieldManagerPrivateImpl::onDidInvalidateWithError(bool doRestart)
     Q_EMIT targetDetectionStopped();
 }
 
+void QNearFieldManagerPrivateImpl::onSessionTimer()
+{
+    if (isSessionScheduled)
+        scheduleSession();
+}
+
 QT_END_NAMESPACE
diff --git a/src/nfc/qnearfieldmanager_ios_p.h b/src/nfc/qnearfieldmanager_ios_p.h
index 6aa1574e..b3668ff6 100644
--- a/src/nfc/qnearfieldmanager_ios_p.h
+++ b/src/nfc/qnearfieldmanager_ios_p.h
@@ -54,9 +54,11 @@ Q_SIGNALS:
 private:
     QT_MANGLE_NAMESPACE(QIosTagReaderDelegate) *delegate API_AVAILABLE(ios(13.0)) = nullptr;
     bool detectionRunning = false;
-    bool isRestarting = false;
+    bool isSessionScheduled = false;
+    QTimer sessionTimer;
     QList<QNearFieldTargetPrivateImpl *> detectedTargets;
 
+    void scheduleSession();
     void startSession();
     void stopSession(const QString &error);
     void clearTargets();
@@ -65,6 +67,7 @@ private Q_SLOTS:
     void onTagDiscovered(void *target);
     void onTargetLost(QNearFieldTargetPrivateImpl *target);
     void onDidInvalidateWithError(bool doRestart);
+    void onSessionTimer();
 };